In a known system, for transportation of articles in a clean room or the like, movable bodies are moved using a linear motor having a primary side on the ground, and a secondary side on each of the movable bodies. For example, as the linear motor, an LSM (linear synchronous motor) is adopted. Coils are provided on the ground, and secondary members such as magnets and magnetizable material are provided on the movable bodies. In a large-scale system having a long travel route, loops and transits between the loops are provided. Therefore, the travel route is divided into a plurality of zones, and the linear motor is controlled by a zone controller provided for each zone.
Using linear scales or the like provided on the primary coils of the linear motor, coordinates of the movable bodies based on the linear scales are recognized. However, a technique of determining coordinates of movable bodies relative to the travel route by interconnection of the coordinates of the movable bodies is not known. In this approach, the zone controller controls positions of movable bodies using coordinates based on individual linear scales. Therefore, it is difficult to place a plurality of movable bodies in one zone. It is because positions of the movable bodies are not controlled based on positions on the travel route, but controlled based on positions relative to the coils, and it is difficult to control distances or the like between the movable bodies.
The number of movable bodies per zone represents transportation capability of the system. In this regard, in an attempt to improve the transportation capability, the inventor studied to make it possible to express the position of the movable body in a coordinate system for directly expressing the position on the travel route, without using the coordinate based on the linear scale. As an example of a related art document, Patent Publication 1 (JP2002-337037A) proposes a technique of detecting a position of a movable body using a linear scale.